1) Field of the Invention
The present invention relates to a broadcast service system where a broadcast transmission terminal is connected to a broadcast reception terminal through plural or large number of switching nodes.
2) Description of the Related Arts
Recently, with a progress on the switching technology field, integrated services digital network (ISDN) has been widely spread and has been developed to broad-band (B-) ISDN. It has been expected that future broad-band switching services will be adjusted as communication infrastructure while broadcasting will be expansively utilized as switching services.
Conventional inhouse broadcast servicing means includes (1) wireless broadcasting services utilizing satellite communication, (2) CATV utilizing private lines, and (3) TV conference services utilizing ISDN.
An economic problem occurs because the items (1) and (2) require an independent network in addition to the inhouse network. As for the item (3), the transmission efficiency is poor because an external device controls the whole network.
FIG. 12 is a diagram showing the first example of a conventional broadcast service system. In such a broadcast service system, a broadcast transmission terminal (for example, TV camera shown in FIG. 12) 1 on the transmission side reads an image information to convert into an electric signal and then transmits the image information from the antenna 2 by wireless. On a reception side, the image information is received with the antenna 3-i (i=1.about.N where N is a natural number) to display a desired image on a cathode-ray tube of a broadcast reception terminal (for example, a television set) 4-i. Since plural broadcast transmission terminals 1 have respective allocated channels, each of the plural broadcast reception terminals 4-i can select a desired channel.
FIG. 13 is a diagram showing the second example of the conventional broadcast service system utilizing cable communications. Such a system is used, for example, for television conference systems. Like numerals represent similar elements to those shown in FIG. 12. In such a broadcast service system, the broadcast transmission terminal (for example, a TV camera) 1 on a transmission side reads image information, and converts it into an electric signal to input to multipoint conference device (center) 5. Then the multipoint conference device 5 inputs the received image information to the first switching node 6-1. The switching node 6-1 executes a switching operation to a necessary path in accordance with a destination selection signal sent from the multipoint conference device 5.
Furthermore, the output of the first switching node 6-1 is sent to the second switching node 6-2 which controls a further switching operation to desired paths. The output of the second switching node 6-2 is sent to desired paths. On the reception side, respective broadcast reception terminals (for example, TV sets) 4-i receive image information to display it on CRTs. This example shows only two switching nodes, but a desired number of switching nodes may be arranged.
The broadcast service system shown in FIG. 14 may be considered. In this example, the image information read by the broadcast transmission terminal 1 on the transmission side is inputted to a terminal adapter (TA) 10 to convert into an asynchronous transfer mode (ATM) cell. In order to execute an ATM conversion by the terminal adapter 10, broadcast information, transmission information, and a channel number N are added to the header portion of the information. The added information can identify a specific broadcast transmission terminal 1, when the image information from plural broadcast transmission terminals 1 are converted into ATM cells.
The output of the terminal adapter 10 is sent to the distribution module 13 via the first ATM switching node 11-1. The ATM switching node 11-1 is connected to the distribution module 13 through a subscriber line signal interface. The distribution module 13 can be regarded as an ISDN terminal when it is viewed from the ATM switching node 11-1.
Respective broadcast reception terminals (in this example, a TV set) 4-i on the reception side transmit a feature access code to the ATM switching node 11-2 for requesting information of broadcast/reception/channel N. When the ATM switching node 11-2 receives the feature access code, it makes paths corresponding to the number of received broadcast reception terminals and has access to the distribution module 13 via the first ATM switching node 11-1, whereby desired image information can be received.
In the current broadcast service systems described above, it is general to execute a connection control using the multipoint connection device as shown in FIG. 13. In this case, since the distribution function is converged on the center side, when communication is made through plural switching nodes, the connection paths between broadcast reception terminals and multipoint connecting devices are needed between switching nodes to the number of broadcast reception terminals. Since the connection status enables only an uni-directional communication to the center side, the broadcast services for plural contents cannot be realized.
Moreover, when the broadcast service system shown in FIG. 14 is used, the distribution module 13 connected to the ATM switching node 11-1 copies a cell and transmits it to the ATM switching node 11-2, the connection paths are needed between the switching nodes 11-1 and 11-2 by the number of broadcast reception terminals. Therefore there is a disadvantage in that the transmission efficiency between the switching nodes 11-1 and 11-2 is poor.